Cylinder charge temperature control for an internal combustion engine

ABSTRACT

A method of operating an engine is provided. The engine includes at least one cylinder communicating with an intake manifold via an intake manifold valve and an exhaust manifold via an exhaust manifold valve, the cylinder including a piston arranged within the cylinder, wherein the piston is coupled to a crankshaft of the engine. The method comprises discontinuing combustion in the cylinder during a plurality of cycles of the engine; during the plurality of cycles, operating the exhaust manifold valve and the intake manifold valve to provide a net flow of gases from the exhaust manifold to the intake manifold via the cylinder and adjusting a torque signature provided to the crankshaft during each cycle by the piston responsive to an operating condition.

BACKGROUND AND SUMMARY

Some engines may be configured to perform what may be referred to ascontrolled auto-ignition (CAI), whereby a mixture including air and fuelis auto-ignited during a compression stroke of the cylinder's pistonwithout necessarily requiring a spark or a pilot injection to initiatecombustion. One particular type of controlled auto-ignition known ashomogeneous charge compression ignition (HCCI) includes auto-ignition ofa substantially homogenous mixture of air and fuel. HCCI may be used toachieve improved engine efficiency and reduced emissions, under someconditions. However, under other conditions, it may be difficult toachieve auto-ignition or to control the timing of auto-ignition. Forexample, during certain higher or lower engine torque or engine speedranges, auto-ignition may be difficult to control resulting in misfire,engine knock, or pre-ignition.

One approach to address this issue includes the use of chargetemperature control to extend the operating range of auto-ignition. Asone example, exhaust gases may be recirculated from the exhaust manifoldto the intake manifold via an external exhaust gas recirculation (EGR)passage. These EGR gases may be used to provide charge heating, wherebythe amount of EGR gases supplied to the cylinders may be adjusted tocontrol the timing of auto-ignition. In this way, HCCI mode operationmay be extended. However, the inventors of the present disclosure haverecognized that this approach utilizes additional hardware including anEGR passage, EGR valves, and additional control systems, therebyincreasing the cost or complexity of the engine system. As anotherexample, a portion of the exhaust gases retained by each cylinder may becontrolled by varying the timing of an exhaust valve of the cylinder.However, the inventors herein have recognized that this approach maystill not provide sufficient charge heating during some conditions. Forexample, during lower engine load conditions, the cylinder may notretain sufficient heat to enable auto-ignition.

Another approach that may be used to extend HCCI operation to lower loador torque ranges includes the practice of deactivating some of theengine cylinders, thereby increasing the effective load at the activecylinders. However, the inventors have recognized that this approach mayresult in increased noise and vibration harshness (NVH), under someconditions.

In order to address some of these and other issues, the inventors hereinhave provided a method of operating an engine. The engine includes atleast one cylinder communicating with an intake manifold via an intakemanifold valve and an exhaust manifold via an exhaust manifold valve,the cylinder including a piston arranged within the cylinder, whereinthe piston is coupled to a crankshaft of the engine. The methodcomprises discontinuing combustion in the cylinder during a plurality ofcycles of the engine; during the plurality of cycles, operating theexhaust manifold valve and the intake manifold valve to provide a netflow of gases from the exhaust manifold to the intake manifold via thecylinder and adjusting a torque signature provided to the crankshaftduring each cycle by the piston responsive to an operating condition.

In this way, exhaust gases produced by the first cylinder may bereturned to the intake manifold via at least a second cylinder wherethey may be used to provide charge heating for subsequent combustionevents by the first cylinder while the second cylinder can provide atorque signature to the crank shaft. Thus, NVH may be reduced or enginebraking may be performed, for example, during a deactivated state of thesecond cylinder. Note that combustion in the first cylinder is notlimited to auto-ignition, and that other types of combustion may beperformed by the first cylinder.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A, 1B, and 1C show net flow for each cylinder of example engines.

FIG. 2 shows a detailed view of a cylinder of an example engine.

FIG. 3 shows an example mode map for an engine.

FIG. 4 shows a high level flow chart depicting an example engine controlstrategy.

FIG. 5 shows a flow chart depicting an example engine control strategyfor varying the temperature of exhaust gases or heated air that isprovided to the intake manifold via at least one cylinder.

FIG. 6 shows a flow chart depicting an example engine control strategyfor varying the flow rate of exhaust gases or heated air that isprovided to the intake manifold via at least one cylinder.

FIGS. 7-13 show timing diagrams for an example engine.

FIG. 14 is a graph depicting an example of how the level of chargeheating provided to cylinders performing auto-ignition may be variedresponsive to operating conditions.

FIG. 15 is a flow chart depicting an example engine control strategy fordeactivating or reactivating engine cylinders.

FIG. 16 is a graph depicting an example of how the number of deactivatedcylinders may be varied with an operating condition such as engine load.

FIG. 17 is a flow chart depicting an example engine control strategy foradjusting the auto-ignition timing for a first cylinder group.

FIG. 18 is a flow chart depicting an example engine control strategy forselecting a charge heating mode for a cylinder based on a deactivatedstate of the cylinder.

FIG. 19 is a timing diagram for an example engine.

FIG. 20 is a timing diagram showing example torque pulsations for acylinder providing net flow of gases from the exhaust manifold to theintake manifold.

DETAILED DESCRIPTION

Charge heating for a first group of cylinders of an internal combustionengine will be described. As one example, charge heating may be providedby supplying gasses of increased temperature including at least one ofexhaust gases and heated intake air to an intake manifold of the firstcylinder group via a second cylinder group. The first and secondcylinder groups may each include one or more cylinders. Each cylinder ofthe second cylinder group can provide a net flow of exhaust gases to theintake manifold from the exhaust manifold or temporarily trap intake airfrom the intake manifold where it may be reintroduced after being heatedby the cylinder. The heated gases provided to the intake manifold by thesecond cylinder group may be entrained by the first cylinder group toincrease the charge temperature of these cylinders, which may bebeneficial for some combustion modes. As one non-limiting example,charge heating may be used enable auto-ignition in the first cylindergroup and/or to vary the timing of auto-ignition in the first cylindergroup.

FIG. 1A shows an example engine 10A including a plurality of combustionchambers or cylinders 30. Engine 10A can receive intake air via anintake passage 42 communicating with intake manifold 44. The amount ofair supplied to the cylinders of the engine can be controlled byadjusting a position of throttle 64 and/or one or more intake manifoldvalves coupled to the cylinders, which are shown in greater detail inFIG. 2. Engine 10A can exhaust combustion products via an exhaustmanifold 46 communicating with exhaust passage 48. Exhaust passage 48can include an exhaust after-treatment device 70. Thus, as shown by FIG.1A, net flow of the engine if from intake passage 42 through engine 10Ato exhaust passage 48, where it may be exhausted to the surroundingenvironment.

As indicated by FIG. 1A, engine 10A includes a plurality of cylindersincluding a first cylinder group denoted as Group A and a secondcylinder group denoted as Group B. In this example, each cylinder of thefirst cylinder group (Group A) provides a net flow of gases from intakemanifold 44 to exhaust manifold 46. In contrast, each cylinder of thesecond cylinder group (Group B) provides a net flow of gases fromexhaust manifold 46 to intake manifold 44. For example, Group B cantransfer exhaust gases from the exhaust manifold to the intake manifold,where they may be entrained by the cylinders of Group A in addition tointake air received via intake passage 42. Thus, while the net flowthrough engine 10A is from the intake passage to the exhaust passage,some of the cylinders can provide a net cylinder flow from exhaustmanifold 46 to intake manifold 44. In this way, heated gases includingexhaust gases may be supplied to the intake of the Group A cylinders viathe cylinders of Group B.

Furthermore, the cylinders of Group B can further increase thetemperature of the gases provided to the intake manifold by performingcombustion with these gases. Thus, in some examples, combustion in eachcylinder of Group B may be discontinued, while in other examples,combustion may be performed in each cylinder of Group B. In someexamples, the cylinders of Group A may utilize at least a portion of thegases supplied to the intake manifold via the cylinders of Group B toperform auto-ignition.

While FIG. 1A shows Group A including three cylinders and Group Bincluding one cylinder, it should be appreciated Groups A and B mayinclude different numbers of cylinders in other examples. Furthermore,the position of the cylinder of Group B relative to the position of thecylinders of Group A can be different. For example, the cylinder ofGroup B can be between two cylinders of Group A. The distribution ofgases provided to the intake manifold via the cylinders of Group B canbe adjusted by varying the position of the cylinders of Group B relativeto the cylinders of Group A. In this way, the distribution of exhaustgases provided to the intake manifold can be adjusted so that thecylinders of Group A receive substantially the same mixture of intakeair and the exhaust gases.

FIG. 1B shows an example engine 10B including two banks of cylindersdenoted 14 a and 14 b. Engine 10B can receive intake air via intakepassage 42 communicating with intake manifold 44A/B. While engine 10B isshown in FIG. 1B to include a common intake manifold, it should beappreciated that in some embodiments, engine 10B may include separateintake manifold so that engine bank 14 a receives intake air via intakemanifold 44A and engine bank 14 b receives intake air via intakemanifold 44B. Thus, the common intake manifold of FIG. 1A is denoted by44A/B. The amount of air supplied to the engine cylinders can becontrolled by adjusting a position of throttle 64 and/or one or moreintake manifold valves coupled to the cylinders, which are shown ingreater detail in FIG. 2.

Engine bank 14 a can exhaust combustion products via an exhaust manifold46A communicating with exhaust passage 48A. Exhaust passage 48A caninclude an exhaust after-treatment device 70A. Similarly, engine bank 14b can exhaust combustion products via an exhaust manifold 46Bcommunicating with exhaust passage 48B. Exhaust passage 48B can includean exhaust after-treatment device 70B. Finally, exhaust passages 48A and48B can combine at exhaust passage 50. However, in some embodiments,exhaust passages 48A and 48B may not be combined. Thus, as shown by FIG.1B, net engine flow is from intake passage 42 through banks 14 a and/or14 b of engine 10B to exhaust passage 50, where it may be exhausted tothe surrounding environment.

As indicated by FIG. 1B, engine 10B includes a plurality of cylindersincluding a first cylinder group denoted as Group C and a secondcylinder group denoted as Group D. The first group of cylinders (GroupC) and the second group of cylinders (Group D) may be included with eachbank of the engine. However, in some embodiments, bank 14 a may includea different quantity of cylinders of the first cylinder group and secondcylinder group than bank 14 b. In this example, each cylinder of thefirst cylinder group (Group C) of bank 14 a provides a net flow fromintake manifold 44A to exhaust manifold 46A and each cylinder of thefirst cylinder group of bank 14 b provides a net flow from intakemanifold 44B to exhaust manifold 44B. In contrast, each cylinder of thesecond cylinder group (Group D) provides a net flow from exhaustmanifold 46A to intake manifold 44A for bank 14 a and from exhaustmanifold 46B to intake manifold 44B for bank 14 b. Thus, while the netflow through engine 10B is from intake passage 42 to exhaust passage 50,some of the cylinders can provide a net cylinder flow from exhaustmanifolds 46A or 46B to intake manifolds 44A or 44B.

Furthermore, the cylinders of Group D can further increase thetemperature of the gases provided to the intake manifold by performingcombustion with these gases. Thus, in some examples, combustion in eachcylinder of Group B may be discontinued, while in other examples,combustion may be performed in each cylinder of Group B. In someexamples, the cylinders of Group C may utilize at least a portion of thegases supplied to the intake manifold via the cylinders of Group D toperform auto-ignition.

FIG. 1C shows engine 10A as described with reference to FIG. 1A. In thisexample, a first group of cylinders (Group E) provides a net flow ofgases from the intake manifold to the exhaust manifold, while a secondgroup of cylinders (Group F) temporarily traps gases received from theintake manifold, where they are heated within the cylinders of Group F,and are returned to the intake manifold where they may be entrained bythe cylinders of Group E.

Furthermore, the cylinders of Group F can further increase thetemperature of the gases provided to the intake manifold by performingcombustion with these trapped gases. Thus, in some examples, combustionin each cylinder of Group F may be discontinued, while in otherexamples, combustion may be performed in each cylinder of Group F. Insome examples, the cylinders of Group E may utilize at least a portionof the gases supplied to the intake manifold via the cylinders of GroupF to perform auto-ignition.

Each of the approaches shown in FIGS. 1A, 1B, and 1C may be used, forexample, during part load conditions whereby cylinders of the secondgroup may be used to trap, compress, and heat the cylinder charge, withor without combustion, before pushing these gases back into the intakemanifold for use in other cylinders performing auto-ignition. In someembodiments, these cylinders may include electromagnetic orelectromechanical valve actuators to allow trapping of cylinder chargeuntil it is desired to be push it back into the intake. Further, thevariable timing of the exhaust manifold valves can also be used totransfer hot exhaust gases from the exhaust manifold to the intakemanifold. In this way, other cylinders may entrain these gases from theintake manifold to provide charge heating.

FIG. 2 shows a detailed view of an example cylinder from engines 10A and10B of FIGS. 1A, 1B, and 1C. As one example, engines 10A and 10B may beincluded in a propulsion system for a passenger vehicle. Engines 10A and10B may be controlled at least partially by a control system includingcontroller 12. Controller 12 can receive an input from a vehicleoperator 132 via an input device 130. In this example, input device 130includes an accelerator pedal and a pedal position sensor 134 forgenerating a proportional pedal position signal PP. Combustion chamber(i.e. cylinder) 30 of engine 10A/B may include combustion chamber walls32 with piston 36 moveably disposed therein. Piston 36 is coupled tocrankshaft 40 so that reciprocating motion of the piston is translatedinto rotational motion of the crankshaft. Crankshaft 40 may be coupledto at least one drive wheel of the vehicle via an intermediatetransmission system. Alternatively, crankshaft 40 may be coupled to agenerator for producing electrical energy, for example, where the engineis used in hybrid electric vehicle (HEV) or with generator applications.Further, a starter motor may be coupled to crankshaft 40 via a flywheelto enable starting of the engine.

Combustion chamber 30 may receive intake air from intake passage 42 viaintake manifold 44 and may exhaust combustion gases via exhaust manifold46 during operation where the cylinder provides net flow to the exhaustmanifold. However, where the cylinder provides net flow to the intakemanifold, exhaust gases produced by combustion chamber 30 or entrainedfrom the exhaust manifold and/or air heated by the combustion chamberwalls 32 may be exhausted to intake manifold 44 as will be describe ingreater detail with reference to FIG. 4. Intake manifold 44 and exhaustmanifold 46 can selectively communicate with combustion chamber 30 viarespective intake manifold valve 52 and exhaust manifold valve 54,respectively. In some embodiments, combustion chamber 30 may include twoor more intake manifold valves and/or two or more exhaust manifoldvalves.

Intake manifold valve 52 may be controlled by controller 12 viaelectromagnetic valve actuator (EVA) 51. Similarly, exhaust manifoldvalve 54 may be controlled by controller 12 via EVA 53. During someconditions, controller 12 may vary the signals provided toelectromagnetic actuators 51 and 53 to control the opening and closingof the respective intake and exhaust manifold valves. The position ofintake manifold valve 52 and exhaust manifold valve 54 may be determinedby valve position sensors 55 and 57, respectively. In alternativeembodiments, one or more of the intake and exhaust manifold valves maybe mechanically actuated by one or more cams, and may utilize one ormore of cam profile switching (CPS), variable cam timing (VCT), variablevalve timing (VVT) and/or variable valve lift (VVL) systems to varyvalve opening and closing operation. For example, cylinder 30 mayalternatively include an intake manifold valve controlled via EVA and anexhaust manifold valve controlled via cam actuation including CPS and/orVCT. As another example, cylinder 30 may alternatively include anexhaust manifold valve controlled via EVA and an intake manifold valvecontrolled via cam actuation including CPS and/or VCT.

Fuel injector 66 is shown coupled directly to combustion chamber 30 forinjecting fuel directly therein in proportion to the pulse width ofsignal FPW received from controller 12 via electronic driver 68. In thismanner, fuel injector 66 provides what may be referred to as directinjection of fuel into combustion chamber 30. The fuel injector may bemounted in the side of the combustion chamber or in the top of thecombustion chamber, for example. Fuel may be delivered to fuel injector66 by a fuel system (not shown) including a fuel tank, a fuel pump, anda fuel rail. In some embodiments, combustion chamber 30 mayalternatively or additionally include a fuel injector arranged in intakemanifold 44 in a configuration that provides what may be referred to asport injection of fuel into the intake port upstream of combustionchamber 30, where it may be entrained by the cylinder.

Intake passage 42 may include a throttle 64. In this particular example,the position of throttle 64 may be varied by controller 12 via a signalprovided to an electric motor or actuator 62, a configuration that maybe referred to as electronic throttle control (ETC). In this manner,throttle 64 may be operated to vary the intake air provided to intakemanifold 44. The position of throttle 64 may be provided to controller12 by a throttle position signal TP. Intake manifold 44 and/or intakepassage 42 may include an mass air flow sensor 120 and an air pressuresensor 122 for providing respective signals MAF and MAP to controller12.

Ignition system 88 can provide an ignition spark to combustion chamber30 via spark plug 92 in response to spark advance signal SA fromcontroller 12, under select operating modes. Though spark ignitioncomponents are shown, in some embodiments, combustion chamber 30 or oneor more other combustion chambers of the engine may be operated in acompression ignition mode, whereby auto-ignition is performed without anignition spark. However, in some conditions where auto-ignition isperformed, a spark may be used.

Exhaust gas sensor 126 is shown coupled to exhaust passage 48 upstreamof emission control device 70. Sensor 126 may be any suitable sensor forproviding an indication of exhaust gas air/fuel ratio such as a linearoxygen sensor or UEGO (universal or wide-range exhaust gas oxygen), atwo-state oxygen sensor or EGO, a HEGO (heated EGO), a NOx, HC, or COsensor. Emission control device 70 is shown arranged along exhaustpassage 48 downstream of exhaust gas sensor 126. Device 70 may include athree way catalyst (TWC) or NOx trap, among various other emissioncontrol devices. In some embodiments, during operation of the engine,emission control device 70 may be periodically reset by operating one ormore cylinders of the engine within a particular air/fuel ratio.

Controller 12, as shown in FIG. 2, may be configured as a microcomputer,including microprocessor unit 102, input/output ports 104, an electronicstorage medium for executable programs and calibration values shown asread only memory chip 106 in this particular example, random accessmemory 108, keep alive memory 110, and a data bus. Controller 12 mayreceive various signals from sensors coupled to the engine, in additionto those signals previously discussed, including measurement of inductedmass air flow (MAF) from mass air flow sensor 120; engine coolanttemperature (ECT) from temperature sensor 112 coupled to cooling sleeve114; a profile ignition pickup signal (PIP) from Hall effect sensor 118(or other suitable type) coupled to crankshaft 40; throttle position(TP) from a throttle position sensor; and absolute manifold pressuresignal, MAP, from sensor 122. Engine speed signal, RPM, may be generatedby controller 12 from signal PIP. Manifold pressure signal MAP from amanifold pressure sensor may be used to provide an indication of vacuum,or pressure, in the intake manifold. Note that various combinations ofthe above sensors may be used, such as a MAF sensor without a MAPsensor, or vice versa. During stoichiometric operation, the MAP sensorcan give an indication of engine torque. Further, this sensor, alongwith the detected engine speed, can provide an estimate of charge orload (including air) inducted into the cylinder. In one example, sensor118, which is also used as an engine speed sensor, may produce apredetermined number of equally spaced pulses every revolution of thecrankshaft.

Thus, FIG. 2 shows only one cylinder of a multi-cylinder engine, andthat each cylinder may similarly include its own set of intake/exhaustmanifold valves, fuel injector, spark plug, etc.

As one non-limiting example, a first cylinder group of the engine canselectively perform what may be referred to as controlled auto-ignition(CAI), whereby a charge including a mixture of air and fuel isauto-ignited by compression performed by the cylinder's piston withoutnecessarily requiring a spark or a pilot injection to initiatecombustion. One particular type of controlled auto-ignition, known ashomogeneous charge compression ignition (HCCI), may use a substantiallyhomogeneous mixture of air and fuel to achieve auto-ignition of thecylinder charge. During operation of the cylinder in HCCI mode, thecharge can be auto-ignited in various regions of the cylindersimultaneously in contrast to a propagating flame front that typicallyoriginates from a spark or a pilot injection.

HCCI may be used to achieve improved engine efficiency and/or reducedengine emissions under some conditions. However, during otherconditions, it may be difficult to achieve auto-ignition. As one exampleshown also in FIG. 3, during lower engine loads and/or lower enginespeeds, auto-ignition may be difficult to achieve, whereby a more robustmode such as spark ignition can be used. Thus, one approach to addressthis issue includes transitioning some or all of the cylinders from HCCImode to a spark ignition (SI) mode or other suitable mode. However,frequent transitions between HCCI and other modes may result in reducedefficiency and/or increased emissions.

Other approaches have been used to extend HCCI mode into lower engineload and/or lower engine speed regions. As one example, exhaust gasesmay be recirculated from the exhaust manifold to the intake manifold viaan exhaust gas recirculation (EGR) passage arranged external thecylinders. These EGR gases may be used to provide charge heating,whereby the amount of EGR gases supplied to the cylinders may be used toadjust the timing of auto-ignition. In this way, HCCI mode operation maybe extended. However, this approach utilizes additional hardwareincluding EGR passages, EGR valves, and additional control systems.

Still other approaches have been used to extend HCCI mode into lowerengine load and/or lower engine speed regions. For example, some of thecylinders may be deactivated, whereby combustion in the cylinder isdiscontinued. Thus, the amount of torque produced by the other cylindersmay be increased to enable lower load auto-ignition operation. However,this approach may only extend auto-ignition operation so far and may notenable auto-ignition during lower temperature conditions, such as afterstart-up or during lower ambient air temperature conditions.

FIG. 3 shows an example mode map for an engine that may be stored inmemory of controller 12, for example. In this particular example, themap includes a comparison of engine speed as indicated by the horizontalaxis and engine load as indicated by the vertical axis. Note that themap stored in controller 12 may include operating conditions other thanengine speed or engine load. The operating region of the engine isbounded by a wide open throttle (WOT) curve. While the map of FIG. 3 maybe used to describe the operating mode regions of the engine, it alsomay be used to describe the operating mode regions on an individualcylinder basis. Within the region bounded by the horizontal axis,vertical axis, and WOT curve are the SI mode region, HCCI mode region,and the extended HCCI mode region.

Located within the operating region of the engine, is the HCCI region.As shown in the FIG. 3, the HCCI mode region may omit higher engineloads and speeds and lower engine loads and speeds since auto-ignitionmay be difficult to achieve in these operating regions. Surrounding theHCCI mode region is the SI mode region where the more robust sparkignition mode may be used in place of HCCI to achieve reliablecombustion. Note that SI mode may be performed within the HCCI moderegion, under some conditions.

The extended HCCI mode region shown in FIG. 3 indicates the operatingregion where HCCI may be performed by a first cylinder group byproviding net flow of exhaust gases or heated air from a second cylindergroup to the intake manifold of the first cylinder group, as will bedescribed in greater detail with reference to FIGS. 4-6. It should beappreciated that the map of FIG. 3 including the extended HCCI moderegion may be used to explain operation of the engine as a whole, of thefirst cylinder group, or of a single cylinder of the first cylindergroup.

FIG. 4 shows a high level flow chart depicting an example engine controlstrategy that may be used to control the level of charge heatingprovided to the first cylinder group by varying an amount (e.g. flowrate) and/or temperature of exhaust gases or heated intake air that isprovided to the intake manifold of the first cylinder group via at leastanother cylinder of a second cylinder group. For example, as shown inFIGS. 1A, 1B, and 1C, the first and second cylinder groups may eachinclude one or more cylinders.

At 410, the operating conditions may be identified including past,present, and/or future conditions of the engine system. As describedherein, operating conditions may include engine load, engine speed,engine temperature, intake air temperature, ambient air temperature,ambient air pressure, intake manifold pressure, exhaust manifoldpressure, air/fuel ratio, spark timing, valve timing, valve position,throttle position, transmission state, accelerator pedal position, brakepedal position, combustion state of each cylinder, and level of boostprovided by a boosting device such as a turbocharger or supercharger,among other operating conditions.

At 412, it may be judged whether to provide charge heating to at least afirst cylinder of the first cylinder group. While the routine of FIG. 4will be described with reference to a first cylinder and a secondcylinder, these approaches for providing charge heating may be similarlyapplied to all cylinders of the first cylinder group and all cylindersof the second cylinder group, whereby each group includes one or morecylinders.

As one example, it may be judged that the charge heating is to beprovided to the first cylinder when the operating conditions indicatethat auto-ignition may be difficult to achieve without additionalheating of the cylinder charge. For example, the control system mayreference the map of FIG. 3 and/or FIG. 14 stored in memory to identifywhether to provide charge heating for the first cylinder. As indicatedby the map of FIGS. 3 and/or 14, charge heating may be performed for thefirst cylinder when the engine speed and/or engine load are below athreshold and the first cylinder is to carry out combustion byauto-ignition. For example, when the operating conditions of the enginecorrespond to the extended HCCI mode region, charge heating of thecylinders carrying out HCCI may be initiated. However, charge heatingmay be initiated for the first cylinder and other cylinders of the firstcylinder group even when HCCI is not to be performed. For example, thefirst cylinder may be operated in other suitable modes including SI modewhere charge heating is used.

If the answer at 412 is no, the routine may return to 410.Alternatively, if the answer at 412 is yes, the valve timing of thesecond cylinder may be controlled at 414 to provide a net flow of heatedexhausted gases to the intake manifold of the first cylinder.Additionally or alternatively, the second cylinder may be operated totemporarily trap intake air form the intake manifold where it may beheated by the cylinder via heat transfer from the cylinder walls and/orvia combustion, where it may then be released back into the intakemanifold. For example, as shown in FIG. 1A, the cylinder of Group B canprovide net flow of exhaust gases to intake manifold 44 from exhaustmanifold 46, where these exhaust gases may be entrained by the cylindersof Group A, thereby increasing their charge temperature. As anotherexample, as shown in FIG. 1B, a cylinder of Group D can provide net flowof exhaust gases to intake manifold 44A from exhaust manifold 46A or tointake manifold 44B from exhaust manifold 46B depending on theparticular cylinder bank. As yet another example, as shown in FIG. 1C,the intake manifold gases may be trapped, heated, and released back intothe intake manifold. Thus, it should be appreciated that the secondcylinder may be selected such that at least one valve of the secondcylinder communicates with the intake manifold of the first cylinder.

In some embodiments, the operation at 414 may also include adjusting theposition of throttle 64 and/or a level of boost provided by a boostingdevice to vary the intake manifold pressure. Similarly, where theexhaust passage of the engine includes a throttle valve and/or avariable geometry turbine, the position of the exhaust throttle and/orturbine actuator may be adjusted to vary the exhaust manifold pressure.In this way, the pressure difference across the engine between theintake and exhaust manifolds may be controlled to enable at least asecond cylinder to provide net flow of exhaust gases from the exhaustmanifold to the intake manifold.

At 416, it may be judged whether to increase the charge heating for thefirst cylinder. As one example described with reference to FIG. 17,charge heating may be increased to advance auto-ignition timing or toenable auto-ignition via the first cylinder. If the answer at 416 isyes, operating parameters of at least the second cylinder may beadjusted at 418 to increase the temperature of the exhaust gases orheated air supplied to the intake manifold via the second cylinder.Alternatively or additionally, operating parameters of at least thesecond cylinder may be adjusted at 420 to increase the flow rate of theexhaust gases or heated air supplied to the intake manifold via at leastthe second cylinder. Finally, the routine may return.

Alternatively, if the answer at 416 is no, (i.e. charge heating for thefirst cylinder is not to be increased), the routine may proceed to 422.At 422, it may be judged whether to reduce the charge heating for thefirst cylinder. If the answer at 422 is yes, operating parameters of atleast the second cylinder may be adjusted at 424 to reduce thetemperature of the exhaust gases or heated air supplied to the intakemanifold via the second cylinder. Alternatively or additionally,operating parameters of at least the second cylinder may be adjusted at426 to reduce the flow rate of the exhaust gases or heated air suppliedto the intake manifold via at least the second cylinder. Finally, theroutine may return. Adjustments to the temperature and/or flow rate ofexhaust gases or heated air provided to the intake manifold will bedescribed in greater detail with reference to FIGS. 5 and 6.

FIG. 5 shows a flow chart depicting an example engine control strategythat may be used to adjust the temperature of gases including exhaustgases and/or heated intake air supplied to the intake manifold via atleast the second cylinder. At 510, it may be judged whether thetemperature of the exhaust gases or heated intake air provided to theintake manifold should be adjusted. The temperature of the exhaust gasesor heated air provided to the intake manifold may be increased whereadditional charge heating is requested in response to operatingconditions and/or the operating mode of the other cylinders, forexample, as directed by FIGS. 3 and 14. If the answer at 510 is no, theroutine may return. Alternatively, if the answer at 510 is yes, it maybe judged whether combustion in the second cylinder is discontinued. Thedecision of whether to discontinue combustion in a cylinder will bedescribed in greater detail with reference to FIG. 15.

If the answer at 512 is no (i.e. the second cylinder is carrying outcombustion), one or more of operations 514-524 may be performed. Forexample, at 514, spark timing may be adjusted for the second cylinder.As one example, to increase the temperature of the exhaust gasesprovided by the second cylinder to the intake manifold, the spark timingmay be retarded. At 516, the amount of fuel and/or the fuel injectiontiming for the second cylinder may be adjusted. For example, lateinjection or secondary injections of fuel may be performed to increasethe temperature of the exhaust gases produced by the second cylinder. At518, the valve timing for the second cylinder may be adjusted. Forexample, the intake manifold valve of the second cylinder may be openedearlier such as during combustion to increase the heat transfer to theintake manifold. At 520, the period that the gases are retained by thesecond cylinder may be adjusted to vary the temperature of the exhaustgases and/or heated air that is supplied to the intake manifold by thesecond cylinder. For example, where combustion has been discontinued inthe second cylinder, the period of time that the intake air and/orexhaust gases are retained by the second cylinder may be adjusted toincrease or decrease the heat transfer from the cylinder walls to thetrapped gases before exhausting it to the intake manifold via the intakemanifold valve.

At 522, the ratio of exhaust gases from the exhaust manifold and intakeair from the intake manifold that are trapped by the second cylinder maybe adjusted by varying valve timing and/or lift to vary the temperatureof the resulting mixture of these gases that are exhausted to the intakemanifold via the intake manifold valve. For example, to increase thetemperature of the mixture exhausted to the intake manifold by thesecond cylinder, the amount of exhaust gases received by the secondcylinder from the exhaust manifold may be increased relative to theamount of intake air received from the intake manifold. However, theratio of these gases may be limited where combustion is performed in thesecond cylinder. For example, where the exhaust gases do not includesufficient oxygen to enable combustion, additional intake air may beentrained by the second cylinder. At 524, operating parameters of othercylinders such as described with reference to 514-522 for the secondcylinder may be adjusted to vary the temperature of the exhaust gasesprovided to the exhaust manifold by these other cylinders. For example,spark retard and/or late injection timing may be used to increase thetemperature of the exhaust gases produced by the first cylinder or othercylinder providing net flow to the exhaust manifold, where these exhaustgases of increased temperature may be entrained by the second cylinderand ultimately exhausted back into the intake manifold via the intakemanifold valve of the second cylinder.

Alternatively, if the answer at 512 is yes (i.e. combustion in thesecond cylinder is discontinued), then one or more of 520-524 may beperformed. Finally, the routine may return. In this way, charge heatingfor at least the first cylinder of the first cylinder group may beincreased by increasing the temperature of the exhaust gases or heatedair that are supplied to the intake manifold via the second cylinder.

FIG. 6 shows a flow chart depicting an example engine control strategythat may be used to adjust the mass flow rate of exhaust gases or heatedair supplied to the intake manifold. At 610, it may be judged whetherthe flow rate of the exhaust gases or heated intake air provided to theintake manifold is to be adjusted. The flow rate of the exhaust gases orheated air provided to the intake manifold may be increased whereadditional charge heating is requested in response to operatingconditions and/or the operating mode of the other cylinders, forexample, as directed by FIG. 14. If the answer at 610 is no, the routinemay return. Alternatively, if the answer at 610 is yes, one or more ofoperations 612-620 may be performed to increase the flow rate of exhaustgases and/or heated intake air to the intake manifold.

At 612, the valve timing for at least the second cylinder may beadjusted, for example, to permit more or less flow of gases to theintake manifold. At 614, the frequency of the valve events (e.g. pumpingevents) performed by the second cylinder during a cycle of the firstcylinder may be adjusted to increase or decrease the flow rate of gasesprovided to the intake manifold. For example, as shown in FIG. 9, theflow rate of gases to the intake manifold may be increased by performingvalve opening and closing events more frequently. At 616, the overlapbetween intake and exhaust manifold valves for the second cylinder maybe adjusted to vary the net flow rate of gases to the intake manifoldfrom the exhaust manifold. For example, as shown in FIG. 10, the valveoverlap may be increased to increase the flow rate or decreased toreduce the flow rate.

At 618, the pressure difference between the intake manifold and theexhaust manifold may be adjusted to vary flow rate of exhaust gases tothe intake manifold from the exhaust manifold. For example, the intakethrottle position, level of boost provided by a boosting device, ageometry of the exhaust turbine, and/or an exhaust throttle position maybe adjusted to vary the pressure difference between the intake andexhaust manifolds. In some conditions, the flow rate of exhaust gases tothe intake manifold via the second cylinder may be increased byincreasing the pressure of the exhaust manifold relative to the intakemanifold.

At 620, the number of cylinders providing gases to the intake manifoldmay be adjusted. For example, where the second cylinder is operated toprovide heated gases to the intake manifold and an increased flow rateis requested, operating parameters of a third cylinder may be adjustedto provide heated gases to the intake manifold, thereby increasing thenet flow rate of exhaust gases and/or heated intake air to the intakemanifold. Conversely, if the flow rate is to be reduced and the secondcylinder is providing gases to the intake manifold, then operatingparameters of the second cylinder can be adjusted to provide net flow ofgases to the exhaust manifold rather than the intake manifold. Thus, theflow rate of exhaust gases or heated intake air that is provided to theintake manifold may be reduced by reducing the number of cylinders ofthe second group.

In this way, heat may be added to the air entrained from the intakemanifold of the first cylinder by operating at least another cylinder toprovide net flow of exhaust gases or heated intake air to the intakemanifold of the first cylinder. The temperature of the charge formed inthe first cylinder may be controlled by adjusting the mass flow rateand/or temperature of these gases provided to the intake manifold of thefirst cylinder of the first cylinder group via one or more othercylinders of the second cylinder group. Thus, exhaust gases or heatedintake air may be recirculated to the first cylinder without requiringadditional hardware such as EGR passages or EGR valves. However, itshould be appreciated that the approaches described herein may be usedwith EGR hardware to provide additional charge heating in addition tothe heating provided by the second cylinder group.

FIGS. 7-13 show example timing diagrams further illustrating the variousapproaches described herein. While these timing diagrams depict a fourcylinder engine, for example, as shown in FIG. 1A, it should beappreciated that these approaches may be applied to engine having othernumber of cylinders. As one example, the timing diagrams shown in FIGS.7-13 may be applied to each bank of an eight cylinder engine, forexample, as shown in FIG. 1B.

The timing diagram for each of cylinders 1-4 includes a horizontal axisproviding an indication of piston position of the cylinder, which mayalso be indicative of time. In each of FIGS. 7-13, TDC refers to apiston position of top dead center and BDC refers to a piston positionof bottom dead center for the respective cylinder. Furthermore, IMVrefers to an intake manifold valve and EMV refers to an exhaust manifoldvalve of the cylinder. For each of the intake and exhaust manifoldvalves, the position of the valve is indicated on the timing diagram asopen or closed. While a middle position or partially opened condition ofthe valves is shown, it should be appreciated that the followingdisclosure is not limited to valves that have a middle position. Furtherstill, direct fuel injection, spark ignition, and autoignition timingare also shown as the symbols indicated by the key.

Referring specifically to FIG. 7, each of cylinders 1, 2, 3, and 4 arerepetitively carrying out combustion with a firing order of Cylinder 1,Cylinder 3, Cylinder 4, and Cylinder 2. However, in some embodiments,other suitable firing orders may be used. As one example, each ofcylinders 1, 2, 3, and 4 are operating in a four stroke mode includingintake, compression, power, and exhaust strokes. In the example shown inFIG. 7 combustion may be initiated by spark ignition or auto-ignition.For example, where the operating conditions are within the HCCI moderegion of the map shown in FIG. 3, cylinders 1-4 can perform HCCIwhereby the charge is auto-ignited at the appropriate timing. As anotherexample, where the operating conditions are within the SI mode region ofthe map shown in FIG. 3, cylinders 1-4 can perform SI whereby the chargeis spark ignited at the appropriate timing.

Regardless of whether the cylinders are carrying out combustion in SI orHCCI mode, each of the cylinders are providing net flow from the intakemanifold to the exhaust manifold in the example of FIG. 7. For example,for each of cylinders 1-4, at least one intake manifold valve is openedand closed to admit air into the cylinder from the intake manifold. Thecylinder is then fueled by direct injection where it is combusted by oneof spark ignition or auto-ignition depending on the operatingconditions. Finally, at least one exhaust manifold valve is opened andclosed to release exhaust gases from the cylinder into the exhaustmanifold. In this way, each of the cylinders are providing a net flowfrom the intake manifold to the exhaust manifold of the engine.

In contrast, FIG. 8 shows a timing diagram depicting the cylinder chargeheating approach shown in FIG. 1A or for one of banks 14 a or 14 b asshown in FIG. 1B. The firing order in the example shown in FIG. 8 is thesame as the example shown in FIG. 7. However, cylinder 2 is providingnet flow from the exhaust manifold to the intake manifold. Cylinders 1,3, and 4 are providing net flow from the intake manifold to the exhaustmanifold, for example, as shown in FIG. 1A, while repetitively carryingout combustion. Cylinder 2 is able to transfer exhaust gases produced byother cylinders from the exhaust manifold to the intake manifold byopening and closing the exhaust manifold valve to admit air to thecylinder and subsequently opening and closing the intake manifold valveto release exhaust gases from the cylinder.

Cylinder 2 in this example is carrying out combustion by spark ignition,while cylinders 1, 3, and 4 are carrying out combustion by auto-ignitionto perform HCCI mode. Thus, the exhaust gases entrained by Cylinder 2from the exhaust manifold via the exhaust manifold valve typicallycontain oxygen in order to achieve combustion. As such, during theoperation shown in FIG. 8, some of the cylinders providing net flow fromthe intake manifold to the exhaust manifold may be operated with a leanair/fuel ratio to provide increased oxygen to the exhaust manifold. Asone example, the operation shown in FIG. 8 may be performed when theoperating conditions are within the extended HCCI mode region shown inFIG. 3. In some embodiments, Cylinder 2 may discontinue carrying outcombustion while providing net flow of gases from the exhaust manifoldto the intake manifold, for example, as shown in FIG. 9.

Furthermore, the amount of heat or temperature of the exhaust gasessupplied to the intake manifold by Cylinder 2 can be controlled byvarying the valve timing, amount of fuel injected, the timing of fuelinjection, and/or the spark timing. For example, by retarding the sparktiming, the amount heat produced by Cylinder 2 may be increased.Similarly, by retarding the injection timing, or by providing a secondlate injection of fuel, the temperature of the exhaust gases provided tothe intake manifold may be increased. In this way, one or more cylindersof a second cylinder group such as Cylinder 2 can provide net flow ofexhaust gases from the exhaust manifold to the intake manifold of afirst cylinder group to provide increase charge heating, therebyenabling the HCCI mode region to be extended without changing the firingorder of the cylinders.

FIG. 9 shows another example where at least one cylinder of the engineis operated to provide net flow of exhaust gases from the exhaustmanifold to the intake manifold of cylinders carrying out combustion byauto-ignition. However, the example shown in FIG. 9 differs from theexample of FIG. 8 as Cylinder 2 is not carrying out combustion. In otherwords, Cylinder 2 is deactivated in the example of FIG. 8. Thus, duringdeactivation of the cylinder, fueling of Cylinder 2 and spark can bediscontinued.

Since Cylinder 2 of the second cylinder group is operated to provide netflow of exhaust gases from the exhaust manifold to the intake manifoldwhile not carrying out combustion, the amount (e.g. mass flow rate) ofexhaust gases provided to the intake manifold by Cylinder 2 can becontrolled by varying the frequency of the valve events with referenceto the cycle of other cylinders of the engine. For example, during afirst condition where less charge heating is to be provided to otherengine cylinders, Cylinder 2 can be operated with a greater periodbetween valve events as indicated at 910. As one example, Cylinder 2 canbe operated in a four stroke mode with Cylinders 1, 3, and 4. During asecond condition where greater charge heating is to be provided to otherengine cylinders, Cylinder 2 can be operated with a smaller periodbetween valve events as indicated at 920. For example, Cylinder 2 can beoperated in a two stroke mode, while Cylinders 1, 3, and 4 may beoperated in a four stroke mode. Thus, by varying the frequency of theintake and exhaust manifold valve opening and closing events, the flowrate of exhaust gases from the exhaust manifold to the intake manifoldcan be controlled, thereby adjusting the amount of charge heatingprovided to other engine cylinders.

FIG. 10 shows yet another example where at least one cylinder of theengine is operated to provide net flow of exhaust gases from the exhaustmanifold to the intake manifold, where it can be entrained by othercylinders of the engine, for example, during extended HCCI modeoperation. The example of FIG. 10 is similar to the example of FIG. 9 inthat combustion by Cylinder 2 is discontinued while the intake andexhaust manifold valves are operated to provide net flow of exhaustgases to the intake manifold from the exhaust manifold. The differencebetween the example of FIG. 10 and the example of FIG. 9 includes theuse of valve overlap in FIG. 10 to allow exhaust gases to flow from theexhaust manifold to the intake manifold, at least where the exhaustmanifold pressure is greater than the intake manifold pressure.

As one example, where the exhaust manifold pressure is greater than theintake manifold pressure, at least one exhaust manifold valve and atleast one intake manifold valve of Cylinder 2 may be openedsimultaneously to allow exhaust gases to flow from the exhaust to theintake manifold. The amount of overlap indicated by 1010 and 1020 can beadjusted to control the flow rate of exhaust gases from the exhaustmanifold to the intake manifold. For example, the overlap at 1010 and/or1020 can be increased to increase the flow rate of exhaust gases.Further, the pressure difference between the intake and exhaustmanifolds may be adjusted in a variety of ways to provide yet anotherway of controlling exhaust gas flow rate. For example, intakethrottling, exhaust throttling, boosting, and/or variable turbinegeometry may be adjusted to vary the pressure difference between theintake and exhaust manifolds.

FIG. 11 shows yet another example where at least one cylinder of theengine is operated to provide charge heating for other engine cylinders.In this example, also shown in FIG. 1C, at least one cylinder such asCylinder 2 can be operated to receive air from the intake manifold viaan intake manifold valve where it may be heated by the walls of Cylinder2 and/or by combustion performed by Cylinder 2 before it is exhaustedinto the intake manifold via the intake manifold valve. In this example,the exhaust manifold valves remain closed. The approaches described withreference to FIG. 8 may be used to increase the temperature of theexhaust gases. For example, spark timing and fuel delivery timing andquantity can be adjusting to vary the temperature of exhaust gasesproduced by Cylinder 2.

However, as shown in FIG. 12 and also in FIG. 1C, combustion may bediscontinued in Cylinder 2, for example, as described with reference toFIGS. 9 and 10, whereby the intake manifold valve can be operated toadmit intake air into Cylinder 2 from the intake manifold where it istrapped and heated by the cylinder walls before being exhausted backinto the intake manifold. In this example, the exhaust manifold valvesremain closed.

As shown in FIG. 12, the period that air is retained or trapped by thecylinder may be adjusted to vary the amount of heating provided to theair admitted into the cylinder. For example, where a lower amount ofcharge heating is requested, the period may be shorter as indicated at1210, while during other conditions such as where a greater level ofcharge heating is requested, the period may be longer as indicated at1220. By varying the period by which the air is retained within thecylinder, the temperature of the intake air exhausted to the intakemanifold may be adjusted. Furthermore, the amount of air retained by thecylinder may be controlled by adjusting valve timing to vary the flowrate of heated air that is exchanged between Cylinder 2 and the intakemanifold. Thus, both the flow rate and temperature of the air heated byCylinder 2 may be controlled.

Still other examples are possible. FIG. 13 shows an example where theapproaches of FIG. 8 and FIG. 11 are combined to provide additionalcontrol over the flow rate and temperature of the exhaust gases providedto the intake manifold. For example, as indicated by 1210, the intakemanifold valve may be operated in addition to the exhaust manifold valveto vary the contribution of air received from the intake manifold andexhaust gases received from the exhaust manifold. Similarly, asindicated by 1220, the exhaust manifold valve may be operated inaddition to the intake manifold valve to vary the contribution of airreceived from the intake manifold and exhaust gases received from theexhaust manifold. In this way, combustion may be performed by Cylinder 2even where the exhaust gases received from the exhaust manifold do notcontain excess oxygen, such as where the other cylinders that providenet flow of exhaust gases to the exhaust manifold are operated atstoichiometry or rich of stoichiometry. Note that this approach may beperformed without combustion, for example, to combine the approaches ofFIGS. 9, 10, and 12.

FIG. 14 is a graph showing the level of charge heating that may beprovided to cylinders of the first cylinder group by the second cylindergroup with varying engine speed and/or load to achieve auto-ignition. Asshown in FIG. 14, the amount of charge heating may decrease withincreasing engine load and/or speed, at least during the extended HCCIregion shown in FIG. 3. For example, at 412 of FIG. 4 where it is judgedwhether to perform charge heating, the control system may reference alook-up table or map as described by FIG. 14 stored in memory of thecontroller. Note that the level of charge heating may vary with otheroperating conditions other than engine load and speed, and may benegatively correlated with some of these operating conditions.

FIG. 15 is a flow chart depicting a routine for controlling thedeactivation or reactivation of one or more engine cylinders. Asdescribed herein, deactivation of a cylinder includes discontinuingcombustion in the cylinder, which may include discontinuing fueldelivery to the cylinder and/or discontinuing spark produced by a sparkplug of the cylinder for one or more engine cycles. Note that with adeactivated cylinder, the piston and associated intake and exhaustmanifold valves can still be operated to provide a flow of gases to theintake manifold for charge heating. At 1510, the operating conditionsmay be identified, for example, as described with reference to theoperation at 410 of FIG. 4. At 1512, it may be judged whether todeactivate one or more cylinders of the engine based on the identifiedoperating conditions.

As one non-limiting example, one or more cylinders of the engine may bedeactivated or alternatively reactivated in response to engine load. Forexample, the control system of the engine may reference a look-up tableor map stored in memory in order to judge whether to deactivate orreactivate engine cylinders. FIG. 16 is a graph depicting an exampleengine control strategy that may be implemented by the control system tocontrol the number of deactivated cylinders. As shown in FIG. 16, forexample, at 1610, the number of deactivated cylinders may increase withdecreasing engine load, thereby enabling increased engine efficiencyand/or reduced emissions. Furthermore, by deactivating one or morecylinders, the other cylinders of the engine that are carrying outcombustion may be operated to produce additional torque. Thus, cylindersthat are performing auto-ignition may be operated at a load that iswithin the HCCI mode operating region for the particular cylinder,thereby reducing need for transitioning these cylinders to othercombustion modes such as SI.

Returning to FIG. 15, if the answer at 1512 is judged yes (i.e. one ormore cylinders are to be deactivated), for example, in response toengine load or other operating condition, the routine may then proceedto 1514. At 1514, a cylinder deactivation strategy may be identifiedbased on the operating conditions to reduce noise and vibrationharshness (NVH) of the engine system and/or vehicle driveline whileenabling auto-ignition in cylinders carrying out combustion. Forexample, the control system may identify a range of the number ofcylinders that may be deactivated while enabling auto-ignition in othercylinders of the engine carrying out combustion and meeting enginetorque demands. As shown in FIG. 16, a range of the number of cylindersthat may be deactivated may include a lower bound indicated at 1630 andan upper bound indicated at 1620 surrounding the number of deactivatedcylinders indicated by 1610 for a given operating condition such asengine load or engine torque. As one example, the lower range indicatedat 1630 can correspond to the lower boundary of the HCCI mode regionshown in FIG. 3 for the cylinders of the engine carrying out combustionby auto-ignition. Similarly, the upper range indicated at 1620 cancorrespond to the upper boundary of the HCCI mode region shown in FIG.3. The control system can select a number of deactivated cylinderswithin the range bounded by 1620 and 1630 in order to reduce NVH. Forexample, NVH may be greater among certain combinations of deactivatedcylinders and cylinders carrying out combustion. Furthermore, theposition of the deactivated cylinder relative to the other firingcylinders may be selected to provide reduced NVH. In this way, NVH maybe reduced while enabling auto-ignition in other cylinders of theengine.

At 1516, the frequency and/or volume of the pumping events performed bythe deactivated cylinders may be adjusted to vary the amount of exhaustgases or heated air that is supplied to the intake manifold via thedeactivated cylinders. For example, as described with reference to FIGS.4-6 and as shown in FIG. 9, the frequency at which the deactivatedcylinders trap and release intake air from the intake manifold or trapexhaust gases from the exhaust manifold may be varied to control theflow rate of these gases that are supplied the intake manifold.Similarly, the volume of these gases that are trapped by the deactivatedcylinders may be varied by controlling valve timing to increase ordecrease the flow rate of these gases to the intake manifold. In thisway, the amount of charge heating provided to the cylinders carrying outcombustion may be adjusted in response to the number of deactivatedcylinders.

For example, where an eight cylinder engine is initially operated withtwo deactivated cylinders each providing exhaust gases to the intakemanifold from the exhaust manifold of the engine at a frequency of onceevery 360 crank angle degrees, deactivation of two more cylinders mayresult in a reduced pumping frequency of once every 720 crank angledegrees for the four deactivated cylinders if the same amount of chargeheating is requested.

Returning to FIG. 15, if the answer at 1512 is no (i.e. no cylinders areto be deactivated), then the routine may proceed to 1518. At 1518, itmay be judged whether to reactivate one or more cylinders based on theoperating conditions identified at 1510. If the answer at 1518 is no,the routine may return to 1510. Alternatively, if the answer at 1518 isyes, the cylinder reactivation strategy may be identified by the controlsystem at 1520 based on the operating conditions to reduce NVH whileenabling auto-ignition in cylinders carrying out combustion. Further,the routine may proceed to 1516 to vary the frequency and/or volume ofthe pumping events performed by the deactivated cylinders (if any) tovary the flow rate of exhaust gases or heated air to the intakemanifold. Note that the frequency and/or volume of the pumping eventsperformed by the remaining deactivated cylinders may be increased inresponse to the loss in charge heating provided by the reactivatedcylinders.

FIG. 17 is a flow chart depicting a routine for controllingauto-ignition timing of a first group of cylinders by varying an amountof charge heating provided to the intake manifold via a second group ofcylinders. At 1710, it may be judged whether to perform combustion byauto-ignition in the first group of cylinders. For example, the controlsystem may initiate auto-ignition in the first group of cylinders whenthe operating conditions are within the HCCI mode region or extendedHCCI mode region. If the answer at 1710 is no, the routine may return to1710. Alternatively, if the answer at 1710 is yes, it may be judged at1712 whether the auto-ignition timing is to be advanced relative to itscurrent timing.

The control system may advance or retard the auto-ignition timing inresponse to operating conditions. In at least some conditions, thecontrol system may control the auto-ignition timing so that it occursaround TDC of the cylinder, for example, as shown in FIGS. 7-13.Further, the control system may advance the auto-ignition timing toreduce misfires, or retard the auto-ignition timing to reducepre-ignition and/or knock.

If the answer at 1712 is yes, the charge heating provided by the secondgroup of cylinders may be increased, for example, as described withreference to operations 416-420 of FIG. 4. Alternatively, if the answerat 1712 is no (i.e. the auto-ignition timing is not to be advanced), itmay be judged at 1716 whether to retard the auto-ignition timing. If theanswer at 1716 is yes, then the charge heating provided by the secondgroup of cylinders may be reduced, for example, as described withreference to operations 422-426 of FIG. 4. If the auto-ignition timingis not to be advanced or retarded, the routine may return.

FIG. 18 is a flow chart depicting a routine for controlling cylinders ofa second cylinder group for providing charge heating to a first cylindergroup. This routine may be performed for each cylinder of the engine. At1810, it may be judged whether the cylinder is a member of the secondcylinder group. If the answer at 1810 is no, the routine may return.Alternatively, if the answer at 1810 is yes, it may be judged at 1820whether the cylinder is deactivated or whether the cylinder is to bedeactivated. If the answer at 1820 is yes, the routine may proceed to1830. At 1830, the intake and exhaust valves of the deactivated cylindermay be operated to provide a net flow of exhaust gases to the intakemanifold of the first cylinder group from the exhaust manifold withoutperforming combustion. Alternatively, if the answer is no (e.g. thecylinder is carrying out combustion); the routine may proceed to 1840.At 1840, at least the intake manifold valves of the cylinder may beoperated to temporarily trap intake air from the intake manifold, thecylinder can perform combustion of a mixture including the trappedintake air and fuel, and the intake manifold valves may be operated toexhaust gases produced by combustion of the mixture to the intakemanifold of the first cylinder group. Thus, combustion may be performedon intake air having a higher oxygen concentration than the exhaustgases, while deactivated cylinders that are not performing combustioncan provide a greater amount of exhaust gases to the intake manifold. Inthis way, charge heating may be provided to a first cylinder group byproviding a net flow of exhaust gases to the intake manifold via adeactivated cylinder and/or intake air may be used to perform combustionand the exhaust gases of the combustion process may be returned to theintake manifold by a firing cylinder of the second cylinder group.

FIG. 19 shows a timing diagram similar to those described with referenceto FIGS. 7-13. In this example, cylinders 1 and 3 are members of a firstcylinder group, while cylinders 2 and 4 are members of a second cylindergroup. Thus, Cylinder 2 and Cylinder 4 are providing charge heating forCylinder 1 and Cylinder 3. For example, Cylinder 2 may be deactivated,while Cylinder 4 may be performing combustion. As described by theroutine of FIG. 18, Cylinder 2 that is deactivated may be operated toprovide a net flow of exhaust gases to the intake manifold of the firstcylinder group from the exhaust manifold. In contrast, Cylinder 4 thatis carrying out combustion can be operated to admit air from at leastone intake manifold valve, perform combustion with the admitted air, andexhaust the products of combustion back into the intake manifold.Further, as shown at 1910, the exhaust valve may be operated to enablesome of the exhaust gases to be used in the combustion process and thetiming of the intake manifold valve may be adjusted accordingly at 1920.Similarly, the exhaust manifold valve may be opened along with theintake manifold valve to provide some of the exhaust gases to both theintake manifold and exhaust manifold.

In some embodiments, where the second cylinder group provides chargeheating to the first cylinder group, the control system can vary theabsolute number of cylinders of the second cylinder group that aredeactivated and the absolute number of cylinders of the second cylindergroup that are performing combustion in response to operatingconditions. Further, the control system can also vary the number ofcylinders of the second cylinder group that are deactivated relative tothe first cylinder group in response to operating conditions. Thus, thecontrol system can vary the absolute and relative numbers of cylindersof the second cylinder group that are (1) performing combustion ontrapped intake air and releasing at least a portion of the combusted airinto the intake manifold, (2) trapping and releasing intake air withoutcarrying out combustion, (3) providing a net flow of exhaust gases tothe intake manifold from the exhaust manifold without combustion, and(4) providing a net flow of exhaust gases to the intake manifold fromthe exhaust manifold while carrying out combustion, responsive tooperating conditions as described herein.

FIG. 20 is a timeline showing how a torque signature delivered to thecrankshaft by a deactivated cylinder of the engine may be varied whileproviding net flow of gases from the exhaust manifold to the intakemanifold of the engine. While in this particular example, the cylinderis operated in a four stroke cycle, it should be appreciated that thestrategies described herein can be applied with two, six, eight or othernumbered stroke cycles. The horizontal axis of the graph indicates timeand the vertical axis for each of examples A-E represents a level oftorque delivered to the crankshaft in comparison to piston position.

Examples A-D show operations where the cylinder's torque signatureincludes at least one stroke of the cycle where torque is absorbed fromthe crankshaft and another stroke of the cycle where torque is returnedto the crankshaft while also providing a net flow of exhaust gases fromthe exhaust manifold to the intake manifold. Example E shows acylinder's torque signature including a greater number of strokes wheretorque is absorbed from the crankshaft than where torque is provided tothe crankshaft, while also providing a net flow of exhaust gases fromthe exhaust manifold to the intake manifold. Thus, examples A-D show anoperation where there is a substantially lower net brake torque (e.g. nonet braking torque) over the duration of the cylinder cycle, whileExample E shows an operation where a greater net brake torque isprovided to the crankshaft over the cylinder cycle.

Example A shows at 2010 how a negative torque (e.g. brake torque) may beprovided to the crankshaft by the cylinder during the first stroke byholding the intake and exhaust manifold valves closed as the pistonmoves toward BDC against a vacuum formed in the cylinder. Next, duringthe second stroke, the torque removed from the crankshaft during thefirst stroke may be recovered at 2012 by the piston as it returns to TDCby holding the intake and exhaust manifold valves closed. During thethird stroke, the exhaust manifold valve (EMV) may be opened and closedas the piston moves toward BDC to trap gases from the exhaust manifoldwithin the cylinder. During the fourth stroke, the intake manifold valve(IMV) may be opened and closed as the piston is moving toward TDC torelease the gases to the intake manifold. In this way, the cylinder canprovide a net flow of gases from the exhaust manifold to the intakemanifold, while a torque signature, including positive and negativetorque pulsations, may be transmitted to the crankshaft by the cylinderduring the first and second strokes of the cycle.

Example B shows a similar approach to Example A, except the torquepulsation is offset by a stroke. Thus, as Example B is applied to a fourstroke operation, the torque pulsation is offset 180 crank angle degreesfrom Example A. Example B shows how during the first stroke, the exhaustmanifold valve may be opened and closed as the piston is moving towardBDC to trap gases from the exhaust manifold within the cylinder. Duringthe second stroke, a negative torque may be provided to the crankshaftat 2014 by the cylinder by holding the intake and exhaust manifoldvalves closed as the piston moves toward TDC due to compression of thegases trapped within the cylinder. Next, during the third stroke, thetorque removed from the crankshaft during the second stroke may berecovered at 2016 by the piston as the trapped gases expands within thecylinder by holding the intake and exhaust manifold valves closed.During the fourth stroke, the intake manifold valve may be opened andclosed as the piston moves toward TDC to expel the trapped gases fromthe cylinder into the intake manifold. In this way, the cylinder canprovide a net flow of gases from the exhaust manifold to the intakemanifold and a torque pulsation may be transmitted to the crankshaft bythe cylinder during the second and third strokes of the cycle whileproviding substantially no net brake torque to the crankshaft over theentire cycle.

Example C shows a similar approach to Example B, except the torquepulsation is offset by a stroke. Thus, as Example C is applied to a fourstroke operation, the torque pulsation is offset 180 crank angle degreesfrom Example B or 360 crank angle degrees from Example A. Example Cshows how during the first stroke, the exhaust manifold valve may beopened and closed as the piston is moving toward BDC to trap gases fromthe exhaust manifold within the cylinder. During the second stroke, theintake manifold valve may be opened and closed as the piston movestoward TDC to expel the trapped gases from the cylinder into the intakemanifold. During the third stroke, a negative torque may be provided tothe crankshaft at 2018 (i.e. torque is absorbed from the crankshaft) bythe cylinder by holding the intake and exhaust manifold valves closed asthe piston moves toward BDC against a vacuum formed within the cylinder.Next, during the fourth stroke, the torque removed from the crankshaftduring the third stroke may be recovered at 2020 by the piston as itmoves toward TDC by holding the intake and exhaust manifold valvesclosed. In this way, the cylinder can provide a net flow of gases fromthe exhaust manifold to the intake manifold and a torque pulsation maybe transmitted to the crankshaft by the cylinder during the third andfourth strokes of the cycle while providing substantially no net braketorque to the crankshaft over the cycle.

Example D shows a similar approach to Example C, except the torquepulsation is offset by a stroke. Thus, as Example D is applied to a fourstroke operation, the torque pulsation is offset 180 crank angle degreesfrom Example C, 360 crank angle degrees from Example B, or 540 crankangle degrees from Example A. Example D shows how during the firststroke, the torque may be recovered at 2024 by the cylinder as thecompressed gases expand as the piston moves toward BDC. During thesecond stroke, the intake manifold valve may be opened and closed whilethe piston moves toward TDC, thereby expelling gases from the cylinderinto the intake manifold. During the third stroke, the exhaust manifoldvalve may be opened and closed while the piston moves toward BDC to trapgases from the exhaust manifold within the cylinder. During the fourthstroke, the trap gases may be compressed as the cylinder moves towardTDC, thereby removing torque from the crankshaft as indicated at 2022.In this way, the cylinder can provide a net flow of gases from theexhaust manifold to the intake manifold and a torque pulsation may betransmitted to the crankshaft by the cylinder during the first andfourth strokes of the cycle while providing substantially no net braketorque to the crankshaft over the cycle.

As will be appreciated in light of the present disclosure, one or moreof examples A-D may be performed to provide a torque pulsation to thecrankshaft by the cylinder during a particular phase of the cycle. Thesetorque pulsations may be selected, for example, to reduce NVH in theengine or vehicle driveline that may be caused by cylinder deactivation,among other causes of NVH. Note also that one or more cylinders may eachbe operated to perform one of examples A-D to reduce NVH. Thus, thetiming at which the torque pulsation of the torque signature isperformed relative to other cylinders may be selected while proving nonet braking torque to the crankshaft and while providing a net flow ofgases from the exhaust manifold to the intake manifold. Therefore,greater flexibility in the number and/or relative location ofdeactivated cylinders of the engine may be possible by varying thetorque signatures that are provided by each of the deactivated cylindersas shown in examples A-D.

Example E shows an example where a net braking torque may be provided tothe crankshaft while also proving a net flow of exhaust gases from theexhaust manifold to the intake manifold. During the first stroke, aroundTDC of the first stroke, the exhaust intake manifold valve may be openedand closed to rapidly expel gases from the cylinder, thereby releasingthe gases compressed by a previous stroke. During the first stroke,torque may be removed from the driveline at 2026 as the piston movestoward BDC against the vacuum formed within the cylinder. Around BDCbetween the first and the second stroke, the intake manifold valve maybe rapidly opened and closed to admit gases from the cylinder, therebydiminishing the vacuum within the cylinder. During the second stroke,torque may be again removed at 2028 from the crankshaft by the pistoncompressing the gases admitted to the cylinder from the exhaustmanifold. Around TDC between the second the third strokes, the intakemanifold valve may be rapidly opened and closed to expel the compressedgases into the intake manifold. During the third stroke, the cylindercan remove torque from the crankshaft at 2030 as piston moves toward BDCagainst a vacuum formed within the cylinder. During the fourth stroke,the intake and exhaust manifold valves can be held closed while thepiston returns to TDC, thereby returning the torque to the crankshaftduring the fourth stroke at 2032 which was removed from the crankshaftduring the third stoke. Thus, in this example, a net brake torque isachieved for the cycle.

Alternatively, for example, as shown at 2034, the exhaust manifold valvemay be opened and closed around BDC between the third and fourth strokesto admit gases from the exhaust manifold. Thus, during the subsequentfourth stroke, the gases may be compressed by the piston as it movestoward TDC, thereby removing torque from the crankshaft as indicated at2036. In this way, the amount of braking torque may be increased ordecreased by varying the number of valve opening events around TDC andBDC during the cycle. For example, the net brake torque may be increasedby opening and closing at least one valve of the cylinder during moreTDC or BDC events, while the net brake torque may be reduced by openingand closing at least one valve of the cylinder during less TDC or BDCevents.

Note that the approaches described herein with reference to examples A-Dmay be used to enable the net brake torque to be offset from that shownin Example E. For example, the intake and exhaust manifold valves may beoperated to provide net braking torque during other strokes, while alsoproviding a net flow of exhaust gases from the exhaust manifold to theintake manifold. In this way, engine braking may be achieved whiletransferring exhaust gases from the exhaust manifold to the intakemanifold.

It should be appreciated that various synergies may be achieved withapproaches described herein. As one non-limiting example, HCCI operationin a first group of cylinders may be enabled by operating a second groupof cylinders to provide heated gases to the intake manifold either bytemporarily trapping and releasing intake air, or by transferring gasesfrom the exhaust manifold to the intake manifold. During conditionswhere the requested engine torque is lower than a threshold of the HCCIoperating mode region, one or more cylinders may be deactivated toextend the HCCI operating range. However, the deactivation of one ormore cylinders may cause increased NVH, under some conditions. Thus,some or all of the cylinders of the second cylinder group may beoperated as described with reference to FIG. 20 to provide torquesignatures that cancel out or reduce the NVH caused by the deactivatedcylinders and/or expand the number of deactivated cylinders or therelative location of the deactivated cylinders within the engine.

Note that the example control and estimation routines included hereincan be used with various engine and/or vehicle system configurations.The specific routines described herein may represent one or more of anynumber of processing strategies such as event-driven, interrupt-driven,multi-tasking, multi-threading, and the like. As such, various acts,operations, or functions illustrated may be performed in the sequenceillustrated, in parallel, or in some cases omitted. Likewise, the orderof processing is not necessarily required to achieve the features andadvantages of the example embodiments described herein, but is providedfor ease of illustration and description. One or more of the illustratedacts or functions may be repeatedly performed depending on theparticular strategy being used. Further, the described acts maygraphically represent code to be programmed into the computer readablestorage medium in the engine control system.

It will be appreciated that the configurations and routines disclosedherein are exemplary in nature, and that these specific embodiments arenot to be considered in a limiting sense, because numerous variationsare possible. For example, the above technology can be applied to V-6,I-4, I-6, V-12, opposed 4, and other engine types. The subject matter ofthe present disclosure includes all novel and nonobvious combinationsand subcombinations of the various systems and configurations, and otherfeatures, functions, and/or properties disclosed herein.

The following claims particularly point out certain combinations andsubcombinations regarded as novel and nonobvious. These claims may referto “an” element or “a first” element or the equivalent thereof. Suchclaims should be understood to include incorporation of one or more suchelements, neither requiring nor excluding two or more such elements.Other combinations and subcombinations of the disclosed features,functions, elements, and/or properties may be claimed through amendmentof the present claims or through presentation of new claims in this or arelated application. Such claims, whether broader, narrower, equal, ordifferent in scope to the original claims, also are regarded as includedwithin the subject matter of the present disclosure.

1. A method for engine cylinders having intake and exhaust manifolds,comprising: operating valves in first and second cylinders to providenet gas flow from the exhaust to the intake manifold via the firstcylinder and from the intake to the exhaust manifold via the secondcylinder, the cylinders carrying out combustion; and adjusting valveopening and closing timings to change a timing of torque pulsations froma first to a second stroke of a 4-stroke-cycle.
 2. The method of claim1, wherein the timing of torque pulsations is changed from providing twotorque pulses during the 4-stroke cycle to providing four pulses duringthe 4-stroke-cycle.
 3. The method of claim 1 wherein the opening andclosing timing of an exhaust valve of the first cylinder is changed froma first piston downward stroke to a second, different, piston downwardstroke of the 4-stroke-cycle, and wherein the timing of torquepulsations is changed in response to engine speed.
 4. A method forengine cylinders, the engine having an intake and exhaust manifold,comprising: discontinuing combustion in a first cylinder; operating asecond cylinder to carry out combustion; operating valves in the firstcylinder to provide net gas flow from the exhaust to the intakemanifold; and adjusting opening and closing timings of the valves tochange a timing of torque pulsations from a first stroke to a secondstroke of a 4-stroke-cycle.
 5. The method of claim 4, wherein the timingof torque pulsations is changed from providing two torque pulses duringthe 4-stroke-cycle to providing four torque pulses during the4-stroke-cycle.
 6. The method of claim 4, wherein the opening andclosing timings of the valves of the first cylinder are changed to varya net braking torque generated by the first cylinder.
 7. The method ofclaim 4, wherein the opening and closing timing of an exhaust valve ofthe first cylinder is changed from a first piston downward stroke to asecond, different, piston downward stroke of the 4-stroke-cycle.
 8. Themethod of claim 4, wherein the second cylinder operates with a net flowof gas from the intake to the exhaust manifold.
 9. The method of claim4, wherein the timing of torque pulsations is changed in response toengine speed.
 10. A method of operating an engine including at least onecylinder communicating with an intake manifold via an intake manifoldvalve and an exhaust manifold via an exhaust manifold valve, thecylinder including a piston arranged within the cylinder, wherein thepiston is coupled to a crankshaft of the engine, the method comprising:discontinuing combustion in the cylinder during a plurality of cycles ofthe engine; during said plurality of cycles, operating the exhaustmanifold valve and the intake manifold valve to provide a net flow ofgases from the exhaust manifold to the intake manifold via the cylinderand adjusting a torque signature provided to the crankshaft during eachcycle by the piston responsive to an operating condition, wherein thetorque signature produced during a cycle of said plurality of cyclesremoves torque from the crankshaft.
 11. The method of claim 10, whereinthe exhaust manifold valve is operated to open and close while thepiston is moving from top dead center to bottom dead center to admitgases from the exhaust manifold into the cylinder.
 12. The method ofclaim 10, wherein the intake manifold valve is operated to open andclose while the piston is moving from bottom dead center to top deadcenter to reject gases from the cylinder into the intake manifold. 13.The method of claim 10, wherein the operating condition includes anumber of cylinders of the engine carrying out combustion.
 14. Themethod of claim 10, wherein the operating condition includes a positionof the cylinder relative to other cylinders of the engine.
 15. Themethod of claim 10, wherein the operating condition includes enginespeed.
 16. The method of claim 10, wherein the operating conditionincludes a level of torque produced by the engine.
 17. The method ofclaim 10, further comprising, operating a second cylinder of the engineto provide a net flow from the intake manifold to the exhaust manifold,and performing combustion in the second cylinder by auto-ignition. 18.The method of claim 10, wherein the torque signature includes a negativetorque pulse and a positive torque pulse.
 19. The method of claim 18,wherein the negative torque pulse is produced by said piston compressinggases within the cylinder and the positive torque pulse is produced byexpanding said compressed gases within the cylinder.
 20. The method ofclaim 18, wherein the negative torque pulse is produced by said pistonexpanding gases within the cylinder and the positive torque pulse isproduced by compressing said expanded gases within the cylinder.